Question

The concentration of a contaminant in large number of soil samples is measured. The mean value of 66 ppm is observed. The standard deviation of the samples is 5 ppm.

What is the probability that a sample concentration is between 61 ppm and 72 ppm?

Answer 1

Solution :

Given that,

mean = = 66

standard deviation = = 5

= 66

= 5

P( 61 < < 72 ) = P(( 61 - 66 ) /5 <( - ) / < ( 72 - 66 ) / 5 ))

= P( - 1 < Z < 1.2 )

= P(Z < 1.2 ) - P(Z < - 1 )

= 0.8849 - 0.1587

= 0.7262

probability = 0.7262